Closed cell foam over interior side of brick cladding?
I’ve attached a quick sketch (not to scale) of what I’m up against, but the basic gist is that I am faced with an exterior porch that was long ago converted to additional conditioned space. It looks like the side walls are fine (framed on the slab), but when they bumped out for a bay window, they muddled it up. It appears that the brick cladding on this porch was placed in contact with the interior framing/sheathing. The sheathing is all but dust at this point, and the framing is rotting from the footing up. Interior finish is T&G wood paneling.
It would be pretty tough to incorporate an air/drainage space between the framing and the brick when working from the inside out, and the exterior is all garden shrubs and trees, not ideal for excavating for weep holes.
My first thought was to remove the rotted walls and reframe over concrete that I would pour to fill that lower section of footing to bring it level with the rest of the slab. Then I thought maybe stop the water from pushing through the brick by applying spray foam to the interior side like some do in basements with stone foundation walls? Now I’m wondering whether that would solve the moisture migration issue, if it even does accomplish that, but just doom the brick to holding moisture and causing spalling problems.
Basically, I’m concerned about the best way to solve the current water issue (yes, gutters and grade slope will be corrected) without causing another problem of a different kind.
I didn’t build it this way, just trying to fix it. Any thoughts?
GBA Detail Library
A collection of one thousand construction details organized by climate and house part
Replies
If, as it appears from your illustration, the bay window walls are below grade, then you need to bring that footing up to the level of the slab. Then you could install 1" of XPS against the inside face of the brick cladding and reframe the wall with 2x3 with no sheathing. The XPS will isolate the framing from the brick, limit thermal bridging and still allow some vapor permeance in both directions (unlike closed cell spray foam).
Justin,
How far below grade is the brick footer?
Can you see the framing bottom plate from inside,and is it below grade ?
Roy,
The framing bottom plate is just about dust at this point. The outside of the porch is surrounded by deep snow at this point, so I can't take an accurate measurement, but I'd guesstimate the level of grade to about even with the porch floor. Maybe a bit below. It appears that the brick footing is maybe 8 to 10 inches below the top of the rest of the porch floor.
Robert - is vapor permeance in both directions really needed in this case, though? Is the concern that water will become trapped in the brick? I only ask because I've typically tried to build walls that aim to dry in only one direction (such as when retrofitting a finished basement in an uninsulated space...foam on the walls insulates, but allows to dry to the inside).
Justin,
This is a complicated situation, and I need to be sure I understand. You're saying that the exterior grade is equal with the porch floor. So how and why did the original builder install a framed wall that begins below grade? Are you sure that you are sketching this accurately?
If your understanding and my understanding are both correct, then it's clear that there shouldn't be any below-grade wall framing. So you'll have to figure out a way to support the porch roof, remove the wall framing, and pour concrete from the lower footing to the top of the slab, just as Robert advised.
As long as your brick wall doesn't get extraordinary water exposure, you should be able to install more foam than Robert advises. If you install 3 or 4 inches of rigid foam on the interior, I think your wall will perform OK.
One other potential problem: most brick veneer walls are stabilized by brick ties that tie the veneer to the wall framing. If your wall framing is rotten, your brick wall may not be stable and may have to be demolished.
Martin,
The snow is being cleared away so that I can confirm the height of the surrounding grade, but the plan is definitely to fill in that lower void with concrete, as Robert has suggested. The part I'm most concerned about is the choice and application of the foam. Specifically, should closed cell foam be used to seal out water vapor, or is a more permeable foam (such as XPS) a better choice because of it's drying potential to both sides. I was picturing closed cell foam (or polyiso rigid foam) against the brick to keep outside water out, and any vapor trapped on the interior side of the foam could dry to the inside. Is the concept of drying to both sides necessary?
Justin,
If I understand the situation, ther are only a couple of feet of brick below a bay type window. The framing under the window is toast. Do yo see any movement related to the window? If not , the brick veneer may be carrying a bit of the load . Is this a 1 story bay or higher? If 1 story- no big deal, couple of feet of wall under a window being supported by a couple of feet of brick. I would simply brace, or transfer the load of the window in to the slab and remove the bad knee wall. Depending on the depth to the footer, pour it solid as noted in Robert and Martin's posts or you could lay CMU if the footer is deeper than you expect. Once the framing is above grade the foam detailing won't be so important. I would recommend wall ties of some sort if the brick under the window is more than a couple of feet above grade. They may already be there when you take the bad wall out.
Justin,
Here's a link to a relevant blog by Joe Lstiburek: Insulation Retrofits on Old Masonry Buildings.
These situations are complicated. I'm still worried about the fact that you have a brick veneer wall -- but that the brick ties aren't tied to anything anymore.
If the brick footing is not below the frost line I would take the entire wall out from under the window and start fom scratch. You could do the whole thing from the inside if trees and plantings are in the way. Supporting the load of a single floor bay window bump out is not difficult at all.